Enhancing Protein Extraction from Streptomycin Fermentation Residue via the Optimization of Reaction Conditions in the Enzyme System

Rich proteins within the streptomycin fermentation residue (SFR) could be recovered through an enzymatic treatment. Our work evaluated the performance of different enzyme systems on protein extraction from SFR. The neutral protease (Neu) had excellent extraction performance compared with that of other enzymes in a single-enzyme (SE) system, i.e., 58% of protein can be extracted by Neu under the conditions of pH = 7, temperature = 50 °C, reaction time = 4 h, moisture content = 96%, and enzyme dosage = 5%. However, the double-enzyme (DE) system (Neu + Lysozyme (Lys)) was more effective in the extraction of protein; the extraction rate of protein could reach 66% when the ratio of Neu to Lys was equal to 1:2 under the conditions of pH = 7, temperature = 50 °C, reaction time = 4 h, moisture content = 96%, and enzyme dosage = 3%. In addition, the concentration of soluble chemical oxygen demand (SCOD) in the extract reached 45.5 g·L^-1 in the Neu-Lys enzyme system, the residue of antibiotics in the extract was as low as 3.2 mg·L^-1, and there were 23 types of amino acids (AAs) in the extract, such as arginine, leucine, tyrosine, methionine, and cystine.